1. Field of the Invention
The present invention relates to a brake control apparatus for a vehicle, capable of releasing a brake operation of main brakes when auxiliary brakes are operated after the main brakes perform the braking operation so as to stop the vehicle while the vehicle is in a follow-up driving state to follow a preceding vehicle.
2. Description of Related Art
A vehicle such as an automobile includes, as a brake apparatus, main brakes mainly operated during traveling and stopping and auxiliary brakes (parking auxiliary brakes) mainly operated during parking. The main brakes are configured to decelerate and stop the traveling vehicle by using brake fluid pressure as a braking force generated corresponding to the operation force applied to the brake pedal by a driver. Further, the auxiliary brakes are configured to maintain a stop condition of the vehicle by a braking operation using a pulling force of wires, which is generated by a parking brake lever provided near a driver's seat or an electric actuator.
In these days, a vehicle having an adaptive cruise control (ACC) system with a preceding-vehicle follow-up function, which is for detecting a preceding vehicle as a follow-up subject of the vehicle and for controlling the vehicle to follow the preceding vehicle. The ACC system includes an automatic brake unit. In a follow-up driving state of the ACC system, when an inter-vehicle distance between the vehicle and the preceding vehicle is less than a predetermined inter-vehicle distance, the automatic brake unit controls the main brakes to perform a braking operation to maintain the inter-vehicle distance to be the predetermined inter-vehicle distance. Further, there is also a known automatic brake unit having an automatic stop function for automatically stopping the vehicle as maintaining a predetermined inter-vehicle distance when the preceding vehicle stops.
Further, regarding the ACC system, there is a known technology for operating parking brakes using an electric parking brake device after the vehicle is stopped and releasing the braking operation of the automatic brake unit in order to save the energy to maintain the braking force while the vehicle is stopped.
For example, JP-A-2007-326399 discloses a technology in which an electric parking brake device operates auxiliary brakes before the vehicle automatically stops. According to the technology disclosed in this document, since the auxiliary brakes are operated before the vehicle is automatically stopped, this helps to set the timing for reducing pressure of the main brakes and releasing the main brakes earlier, and accordingly, the relative operation time and usage frequency of the main brakes can be reduced.
Further, JP-A-2006-306350 discloses a technology for controlling an electric parking brake device to perform a braking operation by auxiliary brakes and then releasing main brakes when it is detected that a driver leaves the vehicle or stops the engine under a stop condition of the vehicle maintained by the main brakes.
According to the technology disclosed in JP-A-2006-306350, since the main brakes are released and the braking condition is maintained by the auxiliary brakes when it is judged that the stop condition of the vehicle will continue for a long period of time, the load applied to the main brakes can be reduced.